Magnetic hard disk drives incorporating longitudinal recording heads are well known. However, conventional longitudinal recording heads suffer from the disadvantage that at high recording densities, e.g., exceeding 40 Gbit/in2, the track width is relatively large. In particular, a track width cannot be defined which is smaller than the head track width plus two times the gap length of the head. This limitation results from side fringing magnetic fields which spread at a distance on the order of the gap length from the both track sides across the track. Decreasing the gap length should reduce this characteristic side fringing region. However, as the gap length is decreased, the magnetic fields in the region of recording media along the track are also reduced. For example, at a 50 nm gap length, the maximum in-plane field component at a 10 nm flying height is less than 10,000 Oe, assuming a high moment (4πMs˜20 kG) pole tip material is used. This field is not sufficient to record transitions clear enough for such high densities. At such high densities recording media are expected to have dynamic coercivity above 5,000 Oe, and approximately two times the coercivity is required to record sufficiently defined transitions. Therefore, there is a trade-off in decreasing the gap length.
The trade-off optimization indicates that the smallest gap length at which the maximum areal density can be achieved using a conventional longitudinal recording head ring structure is approximately 50 nm. Therefore, the smallest track width that can be achieved is approximately 50 nm+2×50 nm=150 nm. Taking into account 20 percent for the track misregistration, the smallest track pitch is approximately 180 nm. Assuming a 2:1 bit cell, the maximum areal density that can be achieved is approximately 40 Gbit/in2.
U.S. Pat. No. 5,621,595 to Cohen discloses a magnetic recording head with a pinched gap which is said to reduce side fringing magnetic fields in the gap region. While the disclosed pinched gap design may reduce side fringing fields, the fields in the track region are also reduced significantly, resulting in the inability to record on high coercivity media. Furthermore, the pinched gap design is extremely sensitive to write currents.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.